Zinc oxide ointment for scraping markup

Your hands won't get sunburn! Why not try Canode from Dapra? Its made for the purpose.

Tony

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Just get the phone # from the web site and call them. The stuff is about $14 per 8 Oz bottle, but they have a $50 minimum order, I think.

The deal with marking dyes is you want something where the pigment has extremely strong color, is either a true liquid or the particles are quite microscopic, and that the pigment and carrier are well mixed. Prussian Blue is just about the best, but the mess is just too much for me. I can tell that Canode is not as good, but it is good enough unless you are using it for telescope mirrors or such optical-level precision.

Jon

I just use Prussian Blue oil color from the local artist shop. Easily accessible and relatively inexpensive. But you are right, it makes quite a mess.

Why not get the real deal from your local auto parts joint? Most of the chains carry Prussian blue in a tube around here. Either located with the Loctite stuff or over in the brake and bearing section. Was less than a buck last time I got some. At that price it isn't worth messing with anything else.

stan

I'm trying to analyze what it is about this goo that is so critically important. We're essentially concerned with nothing more than a pigment in a vehicle.

Pigments: I haven't heard why Prussian blue is any better than the much more common pigments like zinc oxide, titanium dioxide, lampblack, etc.

Vehicle: I haven't seen any explanation for using petroleum grease versus something water-soluble as a vehicle. Indeed, the Dapra product seems to be water-soluble.

Overall, I wonder whether using "real deal" (greasy blue stuff) isn't just a hidebound tradition, like an old painter insisting on oil paint when latex would perform as well and clean up more easily. The fact that some suggest substituting artist paints would seem to support this.

If there is some important principle of scraping involved with Prussian blue, then I'd like to understand it. Otherwise, I would prefer not to have to be dependent on a hard-to-find, overpriced, proprietary product that could be just as well replaced with a preparation made from common materials.

My suspicion is that a 79 cent tube of ointment, or a mix of a bit of toner from a spent laser printer cartridge with some drugstore glycerin, and you might have a very suitable and accessible marking medium for scraping.

You need something very thin yet a different color than the metal. Anything in a grease will be way too thick to use well. More look to a Marks a Lot or other such marking pen for fine coating of the surface. Ordinary marking fluid which is in a lacquer base will also be too thick to use. The idea here is to find the little high spots that are as little as a tenth of a thousandth higher than the surrounding area. Anything that sticks up more than 1/2 of that dimension will be upset and thus will give a bad reading of contact when there actually wasn't any.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works every time it is tried!

Richard J sez: "> If there is some important principle of scraping involved with Prussian

Maybe, but why not stick with the tried and true method? If you've never scraped before you'd have one less variable to deal with if you used traditional methods.

Bob Swinney

Yes, that's why I'm asking here if anyone had any homebrew recipes.

It occurs to me now that these compounds might better incorporate dissolved dyes instead of pigments, something like food coloring in glycerin. A sub-

You want a substance that is non-drying, so a magic marker is out.

Because your hands will end up prussian blue, and i'm Italian :^) , and you don't want greasy stuff that is going to smear all over the place as you scrape. Scraping is very "hands on" the work, especially to detect dust particles on the work prior to spotting. Yes Virginia, even a few particles of dust or lint will mess up your spotting. (It leaves swirly marks) You need a convienient way to wash off the work to re-mark the surface. With Canode, a wet sponge works nicely. With Prussian blue you will need a rag soaked in thinner. I don't need my skin to absorb hazmats if I can avoid it. After you scrape a high spot you want the cast iron scrapings to combine with the spotting compound and get pushed away by the scraper. Prussian blue will smear all over and you will have trouble remembering which spots still need scraping.

In precision scraping, keeping your surface plate clean, and cleaning the work prior to spotting is half the job.

Tony

WD-40 works fine.

Yep, this is why I wear the thinner nitrile gloves when doing spotting/scraping.

Jim

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Hard to find? Prussian blue oil paint is available in any artist's store, inexpensively. Works great.

Jim

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